Sorry, not everyone wants to process the file as a stream, and we support big files to. Let's say that you have 40 concurrent users that all upload files sized 10Mb, having all in streams would make the WebServer use 400Mb memory just for the files.

You can easily create a stream with it:
FileStream stream = new FileStream(Request.Form.GetFile("myFile").Filename, FileMode.Open);

No need to be sorry, in this particular case it was easier for me when I could File.Move it to the correct place.

And my comment to extend System.IO.File was not very informed. I was thinking it was more like the java.io.File class, where an object represents a particular file. I see now that it is a namespace for static operations on files.